1. Technical Field
This application relates to a vascular device and more particularly to a thrombectomy device with an improved intravenous rotatable wire for clearing thrombus from dialysis grafts.
2. Background of Related Art
Hemodialysis is a well-known method of simulating renal (kidney) function by circulating blood. The kidneys are organs which function to extract water and urea, mineral salts, toxins, and other waste products from the blood with filtering units called nephrons. From the nephrons the collected waste is sent to the bladder for excretion. For patients suffering from chronic renal insufficiency, hemodialysis is life saving because it provides a machine to simulate the function of the kidneys, thereby enabling the patients to live independently between dialysis treatments.
In the hemodialysis procedure, blood is withdrawn from the patient's body and transported to a dialysis machine, also commonly referred to as a kidney machine. In the dialysis machine, toxins and other waste products diffuse through a semi-permeable membrane into a dialysis fluid closely matching the chemical composition of the blood. The filtered blood, i.e. with the waste products removed, is then returned to the patient's body.
In one approach, an arteriovenous fistula is created so a high rate of blood flows from the artery into the patient's vein. The blood is then withdrawn directly from the patient's vein (native vein fistula) providing high rates of blood flow. Since this approach requires multiple needle sticks in the vein to withdraw and return the blood, the vein can eventually be damaged beyond usability, blood clots can form and the vein can fail. Once the vein fails, it could no longer be used for access and an alternate site must be utilized.
To avoid the repetitive damage to the vein, dialysis grafts are used. These grafts, typically made of PTFE, are implanted under the patient's skin, typically in the patient's forearm, and the graft is sutured at one end to the vein (venous anastomosis) for outflow and at the other end to the artery (arterial anastomosis) for inflow. The graft is also typically a loop graft to provide greater access area. This graft, which functions as a shunt creating high blood flow from the artery to the vein, enables access to the patient's blood without having to directly puncture the vein. That is, the technician sticks the two needles into the graft to respectively withdraw and return blood to the patient, with the inlet on the arterial side for blood requiring filtration processing and the outlet on the vein side for return of processed blood from the dialysis machine.
The dialysis graft, while providing an advantageous arrangement for hemodialysis, may become inoperable after a period of time due to thrombus or clots formed as a result of the high rate of blood flow through the graft and repetitive injury at the venous anastomosis.
There have been various attempts to break up of clots and other obstructing material in the graft. One approach is through injection of thrombolytic agents such as urokinase or streptokinase. These agents, however, are expensive, require lengthier hospital procedures and run the risks of drug toxicity and bleeding complications as the clots are broken.
Other approaches to breaking up obstructions involve mechanical thrombectomy devices. U.S. Pat. No. 5,766,191 discloses a cage or basket composed of six memory wires that expand to press against the inner lumen to conform to the size and shape of the lumen. This multiple wire device is expensive and can be traumatic to the graft, possibly causing damage, since as the basket rotates at high speeds, the graft is contacted multiple times by the spinning wires. Other risks associated with the basket include the possibility of catching onto the graft itself and tearing the graft as well as catching and tearing the suture at the anastomotic site. Additionally, the basket can become filled with the clot which would then require time consuming withdrawal of the basket, cleaning the basket and reinserting it into the lumen.
U.S. Pat. No. 6,090,118 discloses a wire rotated to create a standing wave to remove thrombus. Pending U.S. patent application Ser. No. 10/113,248 filed Apr. 1, 2002 discloses a rotating wire with a substantially sinuous configuration to create a wave-like rotational device. The single wire is less atraumatic than the aforedescribed basket device since it minimizes contact with the graft wall while still effectively mechanically removing thrombotic material.
The present application is directed to improvements to the thrombectomy device of the foregoing '118 patent and the '248 application. These improvements include the attachment of the atraumatic tip to the distal tip of the rotatable wire and the construction of the rotational wire.